This application claims the priority of German application 198 40 186.8, filed Sep. 3, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a laminated glass pane assembly with electrically controllable reflectance, especially for controlling the entry of sunlight and solar heat into vehicles or buildings.
Pane assemblies with controllable transparency are known for example from German Patent Document DE 36 29 879 C2. The disadvantage of this electrochromic pane assembly is that the transmission is controlled by coloration, i.e., by an absorptive operating mechanism. In the colored state, the solar irradiation is absorbed in the coloring layer and therefore, as desired, does not pass directly into the glazed space. However, as a result of the absorption, the pane itself heats up significantly. This results in an undesired time-delayed indirect heating of the space located behind the glass.
One possibility for controlling the reflectance of thin-film assemblies is described in WO 96/38758. The functional layer consists of a rare earth metal hydride layer with a catalyst cover layer. The switching of the reflection is based on the reversible change of the state of hydration of the layer between a metallic highly reflective dihydride phase and a semiconducting trihydride phase with very low reflection. The switching process is triggered by a catalytic gas reaction with gas containing hydrogen. In this type of control, a double pane with a space in between is required, with the optical properties of the functional layer being switched by changing the gas concentration in the space between the panes. Triggering the switching process into the transparent state requires providing or generating a gas containing hydrogen which is conducted into the space between the panes. The reverse reaction into the reflective state can be accomplished for example by flooding the space with air. However, making this a closed assembly is a difficult process. Another disadvantage of this assembly is that a catalyst layer must be made of a metal such as palladium in order to produce the necessary atomic hydrogen from the molecular hydrogen. This catalyst layer limits the maximum possible optical transmission of the entire assembly to 40 percent. These transmission values are insufficient for many applications. Thus for example 70-75 percent transmission is necessary for motor vehicle applications.
The possibility of electrically controlling these functional layers was previously described only as a laboratory experiment (Notten et al., J. Electrochem. Soc., Vol. 143, No. 10, Oct. 1996). The switching process is triggered in an individual layer by the electrolytic decomposition of an alkaline aqueous electrolyte. For a reversibly switchable closed element, this design is not advantageous since the decomposition of the electrolyte occurs irreversibly with the development of a gas.
To increase the reflection values in the visible spectrum, the material of the functional layer described in WO 96/38758 can be alloyed with magnesium (P. van der Sluis, M. Ouwerkerk, P. A. Duine, App. Phys. Lett., 70 (25), 3356 (1997)).
WO 98/10329 A1 describes an optical switching arrangement with the following layer structure:
a glass pane; PA1 an electroreflective functional layer made of an alloy of the hydride of a rare-earth metal and magnesium; PA1 a catalytically active layer that can operate simultaneously as an antioxidation layer made of metals such as palladium or compounds of the AB.sub.2, AB.sub.3 type whose transparency is relatively low (for example, the transparency of palladium is only about 35 to 40 percent); PA1 a proton-conducting solid electrolyte; PA1 a proton storage layer; and PA1 a transparent conducting coating. PA1 a first glass pane; PA1 an electroreflective functional layer consisting of an alloy of the hydride of a rare earth metal and magnesium; PA1 an antioxidation layer consisting of a proton-conducting transparent oxide or fluoride; PA1 an anhydrous proton-conducting solid electrolyte; PA1 a proton storage layer; PA1 a transparent conducting coating; and PA1 a second glass pane.
European Patent Document EP 0 574 791 A2 teaches a polymer electrolyte membrane made of sulfonated polyether ketones for use in fuel cells.
In Japanese Patent Document JP 07-043 753 A an electrochromic cell is described for controlling the incidence of light through a window in which a tantalum oxide layer is provided to protect the electrochromic functional layer against contact with the organic electrolyte.
A goal of the invention is to provide a laminated glass pane that can be switched reversibly in the visible range (especially in the wavelength range between 300 and 800 nm) between highly transparent and reflective states over many switching cycles by applying a low electrical control voltage.
The laminated glass pane assembly according to preferred embodiments of the invention has the following layer structure:
A laminated glass pane assembly according to the invention functions as follows: when an electrical voltage, typically 2 volts, is applied to the transparent conducting coating and to the functional layer so that the minus pole of the voltage source is connected to the functional layer, positively charged protons migrate from the proton storage layer through the solid electrolyte to the functional layer and are neutralized there, creating atomic hydrogen. By a reversible chemical reaction, the atomic hydrogen is stored in the functional layer so that the material of the functional layer changes from a metallic highly reflective state to a semiconducting state with low reflectivity. If the polarity of the electrical voltage is reversed so that the positive pole is connected to the functional layer, protons form and migrate back into the storage layer through the electrolyte. The functional layer is consequently changed back again to a material with a metallic nature. The catalyst layer of the electroreflective functional layer can be eliminated, which is necessary in the known method of gas control since the proton is reduced at the surface to atomic hydrogen which can diffuse directly into the functional layer.
Therefore, the laminated glass pane assembly according to the invention can be switched reversibly under electrical control between a state of high transmission and a state of high reflectivity. Consequently it is possible to regulate the entry of heat into glazed spaces very effectively. At high levels of solar irradiation, overheating of the object is prevented by reflection at the pane. When warming or light is desired, the pane can be switched to the transparent state which makes possible a high degree of transparency to the solar irradiation.
In the laminated glass pane according to the invention with controlled reflectivity, the pane itself remains cool mainly by reflecting the solar radiation energy. As a result, the degree to which energy penetrates the glazing can be regulated very effectively even under long-term irradiation.
Since the functional layer also forms an electrode for electrical control, a homogeneous extensive and rapid switching process is made possible.
Due to the fact that the functional layer is very close to the outside surface within the laminated structure, the assembly achieves a high degree of efficiency.
With the laminated glass pane according to the invention, reversible switching can be achieved over a number of switching cycles. Only low switching energies of less than 1 Wh/m.sup.2 are required for the switching process.
The laminated glass pane assembly according to the invention can be used in particular as glazing for windows of vehicles or buildings. It can also be used however to control light, for example, in headlight assemblies.
The electoreflective functional layer according to the invention consists of an alloy of the hydrides of a rare earth metal, especially yttrium, gadolinium and samarium, and magnesium. The term "electroreflective" in this application describes a layer whose reflectivity can be changed under electrical control. The percentage of rare earth metal or metals preferably is in the range of 20 to 80 percent, for example Y.sub.30 Mg.sub.70. In the case of yttrium, the reversible switching takes place between the metallic dihydride phase YH.sub.2 and the semiconducting trihydride phase YH.sub.3.
The atomic hydrogen required for the switching process is stored in the storage layer as a proton.
Metal oxides, for example cathodically coloring electrochromic layers including in particular tungsten oxide (WO.sub.3) are very well suited for proton storage. When the protons migrate out of the functional layer into such an electrochromic storage layer, they color the latter, such as blue in the case of WO.sub.3. Since this effect is undesired for many applications, it may be advantageous to modify the electrochromic layer in such fashion that only a slight coloration is produced by the proton storage. This is achieved by mixing the tungsten oxide with titanium oxide (TiO.sub.2).
Other materials that are suitable for the proton storage layer are MoO.sub.3, Nb.sub.2 O.sub.5 and V.sub.2 O.sub.5.
The transport of the protons between the storage layer and the electroreflective functional layer takes place through a proton-conducting solid electrolyte. This electrolyte must be anhydrous in order to prevent any damage to the water-sensitive electroreflective functional layer. In one advantageous embodiment, the electrolyte consists of an oligomer or a polymer of sulfonated polyether ketones (PEK, PEEK) with a mobile proton carrier such as imidazole or pyrazole.
In another embodiment, the electrolyte consists of a copolymer of a acrylamidopropane sulfonic acid (AMPS) and another (meth)acrylic derivative, and mobile proton carriers such as imidazole or pyrazole. Especially advantageous is when methoxypolyethyleneglycol(n)monomethacrylate where n=4 to 13, preferably n=9, is used as the (meth)acrylic derivative where n is the number of ethyleneglycol units.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.